Circuit switching is a method of network switching where a dedicated circuit, e.g., a physical path from transmitter to receiver or a particular time slot on such physical path, is established before and maintained throughout each communication. Circuit switching has long been used for voice communication. However, because of the long circuit setup times and the dedication of switch resources for call duration that are involved with known circuit switching networks, packet switching is typically used for data communication since such communication usually occurs in short, high-rate bursts, with long pauses between bursts. Packet switching networks are characterized in that messages are broken down into standard-size packets which are individually routed through the network and in that computers using sophisticated software packages are employed to perform the packet switching functions at the nodes within the network.
Because of evolving technological advances useful in implementing circuit switching networks and because of the complexity of known packet switching systems, circuit switching is sometimes a preferable alternative for use in many data communication applications. Circuit switching networks are frequently implemented with time-slot interchangers having random access memories wherein digital samples are sequentially written into a sample memory and are read from locations of that memory in the order specified by control words read from a control memory. One limitation on the throughput capacity of such time-slot interchangers is the access speed of the random access memories. Known time-slot interchangers have included double-buffered sample memories wherein during a given time interval or frame, samples are sequentially written into a first sample memory while samples which were written into a second sample memory during the previous frame, are being read from the second memory. Since write access and read access are only required of each memory during alternate frames, the number of accesses per frame for each memory is decreased and the throughput of the time-slot interchanger can be correspondingly increased. With known time-slot interchangers used for voice communication, the contents of the control memory are changed only relatively infrequently. Such changes can be made by dedicating a small portion of each frame, i.e., one or two time slots, for control memory write access. However, when a circuit switching network is to be used in data communication applications requiring that a circuit be established for each packet-sized data communication, many control memory changes may have to be effected during each frame.
Providing control memory read access and write access during alternate halves of each time slot, although allowing needed changes to be made, reduces the maximum throughput of the time-slot interchanger.
In view of the foregoing, a recognized problem in the art is the reduction in throughput capacity of known time-slot interchangers with random access control memories when used in data communication circuit switching applications requiring frequent control memory changes.